I'm curious about this question also. Someone on here must have bought a 1080. Please let us know if it has been worth it to you.[yesnod] What benefits have you noticed?
I have a 2560x1600 screen, which isn't quite up there to 4k res, but it still takes a lot more effort to render than a 1080p. I think the 1080 or 1070 would be a good option and would pair well with my CPU, but always curious to hear update news from people who have done it.